Well first off I don't have it in hand yet. Just won it on an ebay auction. This isn't the newer "Plus" model. It's supposed to be NIB, but it's probably at least a year old already (I assume) and may need a new O2 sensor when or not long after I get it. I did a lot of research before bidding on this kit and read in several places that this analyzer doesn't have to be sent in for calibration. That's one of the reasons that I decided to go with it. After going through the manual I'm not so sure that information was correct.. The B-Smart CO sensor is pre-calibrated, but it doesn't really say anything about the O2 sensor calibration in the manual, just lists the part number. Can anyone who owns one of these analyzers enlighten me on the O2 sensor? Just plug it in and you're done or what?